The Weigh of the World

Michael Fickes | Apr 01, 1999

No matter where a hauler turns, there's a scale manufacturer offering a better way to weigh trash.

Landfills, transfer stations and recycling facilities must weigh trucks and trailers inside and out. For these tasks, manufacturers offer in-ground and body scales, some with National Type Evaluation Program (NTEP) certification, and some providing a reasonable measure of the actual weight to insure that loads meet legal limits.

Commercial haulers weigh loads with body or fork scales designed to monitor legal load limits and to insure that customers aren't heaping on more trash than their contract indicates.

Even residential operations are considering scales, as customers who generate a little trash complain about paying the same rates as customers who throw out a lot of trash.

In each weighing category, there are different scale types. Which is right for your operation? To answer that question, you must assess the benefits and decide which scales best suit your needs -present and future. The following is a primer to help you make wise decisions.

In-Ground Scales In-ground scales for landfills or processing facilities such as transfer stations or recycling centers come in five flavors - mechanical, analog, electro-mechanical, digital and hydraulic. Each has its own maintenance requirements, advantages and disadvantages.

Analog load cell scales have four load cells - one at each platform corner - that change shape whenever the truck drives over the platform. Strain gauges measure the shape change and produce varying electrical currents. The volt variations are measured and totaled by a monitoring device, which uses the data to calibrate the weight.

Finally, hydraulic load cell scales produce changes in water pressure, which can be measured by a single analog or digital load cell located away from the scales. These systems have received positive performance reviews in sloppy, dirty, wet and hazardous environments.

Haulers underload their trucks for a variety of reasons. First, they want to avoid enforcement hassles at weigh stations, transfer stations and landfills monitored by regulatory officials. Also, underloading at facilities that use in-ground scales located away from loading areas is common because drivers don't pass over the scales and detect the insufficient load until they are on the way out, and by then they don't want to go back for more material.

On-board truck body scales also have proven useful for self-loaders, eliminating the need to race back and forth between the scale control and loading equipment.

While underloading a truck lowers maintenance costs and enhances safety, loading to full or near-full capacity maximizes profitability without affecting maintenance or safety significantly.

Manufacturers offer two technologies for weighing during loading: load cells and position transducers.

Load cells are welded to truck frames under the body. When a load is applied, the cells change shape, then transmit an electrical signal through circuitry that converts it to weight.

Position transducers measure changes in the height of the suspension and convert that information into electrical data and then the total weight in pounds. These low-cost devices are bolted onto the truck's suspension system.

This technology gained popularity in trucks designed with air-suspension systems. The transducers measure pressure changes in air-suspensions and convert those changes to electrical impulses and then weight.

Swapping tractors and trailers has caused some confusion in relation to truck scales. To weigh with acceptable accuracy, the axles on the tractor as well as the trailer must be scaled, raising calibration questions when a tractor hooks up to different trailers. Some load cell systems on the market today allow trailer swapping, but the driver may need to enter certain information when a swap occurs. Forgetting to do that or doing it incorrectly can throw off the scales.

At least one position transducer system on the market allows trailer swapping with no driver intervention beyond plugging in the connector that links the tractor scale and the trailer scale.

The earliest fork scales for front-end loaders were strain gauges welded onto the front loader arms, eliminating the need to tinker with the frame of the truck, a procedure that many haulers view as risky.

Load cell technology is a more recent development. Different than strain gauges, this equipment can be bolted and unbolted, and saved when a truck moves out of service.

Load cell technology has led to the development of NTEP legal-for-sale scales that can weigh static loads and in-motion loads.

Residential Truck Scales Los Angeles has been evaluating legal-for-trade scales for residential trucks. To date, the city hasn't approved any of the designs, says Pouria Abbassi, senior system analyst for the city administration.

Nevertheless, manufacturers report that they have begun to research advanced technology for these scales. Early designs include a modification of front-end loader scale systems to fit side and rear loading residential trucks.

At least one manufacturer has introduced a federally certified, semi-automated weigh-in-motion system and recommends the product for weighing recyclable pickups.

Weighing On Your Mind There's no avoiding a weighty decision about scales. In Canada, for example, landfill tipping fees in certain areas have quadrupled in the past five years. While rates may be relatively stable in the United States for now, nothing lasts forever. As landfill space grows more valuable, commercial haulers may seek increasingly accurate scale systems. Likewise, residential haulers eventually will have to consider new ways of doing business.